This invention relates to a method and apparatus for accelerating the flow of solid particles entrained in a carrier gas. The method and apparatus for accelerating solid particles in a carrier gas in accordance with the present invention is particularly well suited for use during recarburization of a metal melt in, for example, the refining of iron into steel.
It is well known that the amount of scrap or other cooling additives which are incorporated into a metal melt during refining by the LD, LBE, and other known processes, substantially depends upon the composition of the melt, the temperature of the batch, and the thermodynamic progression of the refining operation. Typically, the consumption of scrap per ton of liquid melt is approximately 300 kg during the conversion of lean melt, and approximately 400 kg for a phosphorous melt. The overall costs of making steel can be reduced by incorporating proportionally larger amounts of scrap into the melt during the refining processes. Thus, in order to reduce the cost of steel, it is desirable to increase the above discussed proportional amounts of additives i.e., scrap.
One known method of proportionally enlarging the amount of scrap material utilized during refining consists of increasing the degree of postcombustion of the carbon monoxide (CO) evolving from the pool so that the pool or melt will absorb a maximum amount of heat liberated from the scrap. Another prior art method for the efficient utilization of scrap comprises heating the metal pool using supplemental sources of energy. Such energy sources include gas and/or liguid fuels and have been associated with variable success. Alternatively, the supplemental energy sources may comprise adding combustible material in the form of granules of carbonaceous material. Using this technique, carbonaceous materials are incorporated into the bottom of the pool through glass pipes or permeable elements located in the bottom of the converter, or from the top, together with a carrier gas.
It will be appreciated that the addition of scrap and other additives for reducing the cost of producing steel may be made either before blasting or after a first phase of blasting.
Luxembourg Patent Application No. LU 84,444, corresponding to U.S. patent application Ser. No. 544,073, now U.S. Pat. No. 4,519,587 which is assigned to the assignee hereof and incorporated herein by reference, describes a system for delivering solid carbonaceous fuel materials from a blowing lance to a metal pool. The apparatus described therein essentially comprises at least one nonoxidizing compressed gas source, a circuit which supplies granulated carbonaceous material suspended in a carrier gas, at least one circuit which supplies flushing gas, various means for metering different flow rates of the gas and solid particulate streams and means for separately or jointly connected the above described circuits to appropriate conduits which terminate in a blowing lance. In order to achieve adequate absorption of the carbonaceous material by the metal melt, it has been found necessary to ensure that the melt not only have predetermined concentrations of oxygen and carbon, but that the pool also have enough carbonaceous material so as to provide adequate kinetic energy at the output of the lance to effect penetration thereof into the melt. This elevated or high kinetic energy, which is also required in order to avoid premature combustion of the carbonaceous material above the pool, is obtained by the use of a powerful flow of carrier gas. In view of the fact that this jet of gas exerts an undesirable cooling effect, it will be appreciated that the desired quantity of carbonaceous material delivered to the pool must utilize a minimum of carrier gas.
It will be appreciated that in constructing and installing a device used to deliver carbonaceous material into a melt, the limitations of existing equipment must be taken into account. For example, the source of gas to which other devices are added may be an important factor. Also, the lengths of the ducts often control the placement of the cellular regulator and the lance-supporting carriage. Moreover, the lance heads and the lance-supporting carriages may not permit exceeding certain duct diameter in view of dimensioning weight and factors.
Particle size distribution of the carbon material must also be considered in constructing and installing such a delivery device. It is well known, for example, that very fine grains of carbonaceous materials have a tendency to stick together. Experiments have shown that this sticking is due to low kinetic energy at the outlet of the lance. Conversely, relatively larger grains of carbonaceous material have a higher inertia, and the carrier gas will not accelerate the larger grains over a short distance to a desired speed. Moreover, the dimensional configuration of the grains is also of great importance as far as abrasion problems with the ducts are concerned. Further, the nature of the carbonaceous material and the effects of impurities (i.e, humidity, volatile substances) on the combustion in the pool, as well as in the metal batch (i.e., sulfur) are all equally important factors in designing and constructing solid particle delivery devices of the type hereinabove discussed.